The present invention relates to a magneto-resistive device, and to any component, such as a magnetic head, a magnetic recording device, and a magnetic memory, which is provided with said magneto-resistive device.
Magnetic recording-reproducing devices have recently exhibited a significant improvement in recoding density. They are provided with a magnetic recording-reproducing head which requires both a high recording performance and a high reproducing performance.
What is particularly required of magnetic recording heads is technical innovation for (1) a higher sensitivity, (2) a smaller track width, and (3) a smaller reproducing gap.
Higher sensitivity leads to higher recording density. A recording density of the order of 1-10 Gb/in2 relies on the anisotropic magneto-resistive effect (AMR), and a recording density of the order of 10-20 Gb/in2 relies on the giant magneto-resistive effect (GMR), which gives a higher sensitivity. Moreover, it is expected that a much higher recording density of the order of 20-50 Gb/in2 will be attained with the help of advanced GMR, such as specular GMR and NOL-GMR (nano-oxide layer type GMR), which has a highly polarized material or an oxide layer interposed between the interfaces of a GMR structure for producing an increased output through the multiple reflection effect of electron spin.
A magnetic head relying on GMR is disclosed in JP-A No. 358310/1992. This magnetic head, which has a spin valve structure, consists of a pinned layer, a non-magnetic thin film (spacer), a free layer, and a magneto-resistive device. The pinned layer consists of a magnetic body whose magnetization is fixed in a specific direction by an anti-ferromagnetic layer. The non-magnetic thin film is laminated on the pinned layer. The free layer is a magnetic film which is laminated on the non-magnetic thin film. The magneto-resistive device changes in electrical resistance depending on the relative angle of magnetization of the pinned layer and the free layer.
The higher recording density expected in the future needs a reproducing system which is much more sensitive than before. A recording density of the order of 70-150 Gb/in2 will rely on the tunneling magneto-resistive effect (TMR) with an extremely high MR ratio because of its high sensitivity. A higher recording density exceeding 150 Gb/in2 will rely mainly on CPP-GMR (current perpendicular to plane geometry GMR) which works with a detecting current flowing in the direction perpendicular to the film surface. The basic technology of TMR is disclosed in P03-154217 and JP-A 91925/1998. Unfortunately, it needs further improvement in the prevention of breakdown by static voltage (due to the very thin insulator that is important for the characteristic properties), reduced resistance for better S/N ratio, and increased bias.
The conventional CIP-GMR device (current-in-plane GMR, in which the detecting current flows in the in-plane direction of the film) has the following disadvantages. For a high linear recording density, a smaller space is necessary between the GMR device and each of the magnetic shield films arranged above and below it. This results in a thinner insulator between the GMR device and the shield film, which does not provide sufficient insulation. Moreover, the reduced reproducing track width makes magnetic domain control difficult and produces asymmetric output signals.
By contrast, in the case of a CPP-GMR device, the insulation between the shield films is not important because both sides of the device function as electrodes. Therefore, a CPP-GMR device will be considerably free from thermal breakdown due to current and non-linearity caused by the magnetic field. Moreover, it is promising for use with high recording densities because it will increase in output as the device area decreases. Much has been reported about CPP-GMR devices, typically, in JP (PCT) No. 509956/1999 and JP-A No. 221363/1995.